1. Field of the Invention
The present invention relates, in general, to plasma display panels and, more particularly, to a composition for barrier ribs of such plasma display panels and to a method of fabricating such barrier ribs using the composition.
2. Description of the Prior Art
Flat display devices, such as a liquid crystal display (LCD), a field emission display (FED) and a plasma display panel (PDP), have been actively studied in recent, and the technique relative to such display devices has been somewhat actively developed.
FIG. 1 is a sectional view, showing the cell structure of a conventional AC-PDP of the surface discharge type, or the most widely used PDP in recent days. As shown in the drawing, each cell of the conventional AC-PDP comprises upper and lower parallel substrates 1 and 15. The upper substrate 1 is preferably made of a transparent material, such as glass, thus effectively transmitting visible light, while the lower substrate 15 is preferably made of glass or metal. Two sustain electrodes 5, individually consisting of a transparent electrode 3 and a bus electrode 7, are arranged on the lower surface of the upper substrate 1. Such a transparent electrode 3 is preferably made of indium tin oxide (ITO), while such a bus electrode 7 is preferably made of aluminum (Al) or chrome/copper/chrome (Cr/Cu/Cr). A first dielectric film 10, made of PbO, is formed on the lower surface of the upper substrate 1 while covering the sustain electrodes 5. A protection film 12, made of MgO, is formed on the first dielectric film 10 through a vapor deposition process. The objective of the above protection film 12 is to protect the dielectric film 10 from an ion sputtering effect. The above protection film 12 has a high secondary electron generation coefficient when a low ion energy is applied to the surface of the film 12 during a PDP plasma discharging process. The protection film 12 thus effectively reduces the voltage for driving and sustaining the plasma.
An address electrode 17 is positioned on the upper surface of the lower substrate 15, while a second dielectric film 19 is formed on the upper surface of the lower substrate 15 while covering the address electrode 17. Two barrier ribs 21, having a stripe shape, are parallely formed on the upper surface of the second dielectric film 19, with the address electrode 17 being positioned on the lower substrate 15 at a middle position between the two barrier ribs 21. A black matrix 23 is formed on the top end of each of the barrier ribs 21, thus improving the contrast of the PDP. A plurality of phosphor layers 25 are formed on the upper surface of the second dielectric film 19 and are formed on the sidewalls of both the barrier ribs 21 and the black matrixes 23. The above phosphor layers 25 emit R, G and B visible light corresponding to red, green and blue. The phosphor layers 25 are isolated from each other by both the barrier ribs 21 and the black matrixes 23. In the above cell of the PDP, the R, G and B phosphor layers 25 form one pixel. The upper and lower substrates 1 and 15 are, thereafter, integrated into a single structure, thus forming a desired cell of the PDP with discharge spaces being defined by the barrier ribs 21 and being filled with mixed gas, such as Ne+Xe gas.
The above AC-PDP is operated as follows. That is, a constant voltage is applied to the gap between the address electrode and one of the two sustain electrodes, and so the address electrode discharges to select desired display cells. In the case of such an addressing discharge, a wall voltage is generated in each of the selected cells. After the addressing discharge, an AC voltage is applied to the two sustain electrodes at the same time, and so the selected cells perform a sustain discharge to emit visible light. Such a sustain discharge is controlled to change the brightness level in accordance with discharge time.
In the above PDP cell structure, the objective of the barrier ribs 21 is to secure a space for gas discharge between the upper substrate 1 and the lower substrate 15. The formation of the above ribs 21 is also to isolate the phosphor layers 25 from each other, thus partitioning the discharge cells, and to determine the distance between the electrodes for performing discharge, and to prevent crosstalk due to discharge from neighboring cells, and to reflect light from the phosphor layers 25 to the upper substrate 1. In order to accomplish the above-mentioned objective of the barrier ribs 21, the ribs 21 necessarily have a low thermal expansion coefficient, a high thermal stability, a low baking temperature, a dense structure and a low dielectric constant.
In the prior art, such barrier ribs are typically made of PbO--B.sub.2 O.sub.3 --SiO.sub.2 based glass or PbO--B.sub.2 O.sub.3 --SiO.sub.2 based glass, including a large amount of 60.about.80 wt % of PbO. The composition of the above PbO--B.sub.2 O.sub.3 --SiO.sub.2 based glass is given in Table 1.
TABLE 1 Components(wt %) PbO B.sub.2 O.sub.3 SiO.sub.2 Contents(wt %) 60 .about. 80 wt % 5 .about. 15 wt % 15 .about. 20 wt %
Such a conventional barrier rib for PDPs is fabricated as follows. As shown in the processing diagram of FIG. 2, a glass-ceramic material, prepared by mixing an oxide filler with PbO--B.sub.2 O.sub.3 --SiO.sub.2 based glass or PbO--B.sub.2 O.sub.3 --SiO.sub.2 based glass at a predetermined ratio, for example, 4:6.about.7:3, for a predetermined time, is ground at step 31, thus forming a fine mixture powder having a size not larger than 10 .mu.m. In the above step, an Al.sub.2 O.sub.3 and TiO.sub.3 mixture is used as the oxide filler and the composition of Al.sub.2 O.sub.3 and TiO.sub.3 mixture is given in Table 2.
TABLE 2 Components (wt %) Al.sub.2 O.sub.3 TiO.sub.3 Contents(wt %) 95 .about. 100 wt % 0 .about. 5 wt %
Thereafter, the mixture powder from the step 31 is mixed with an organic vehicle, thus forming a paste or a slurry at step 32. In such a case, the organic vehicle is formed by mixing BCA (butyl-carbitol-acetate), BC (butyl-carbitol) and EC (ethyl-cellulose) together at a predetermined mixing ratio. After the step 32, the paste or the slurry is applied to the top surface of the second dielectric film 19 of the lower substrate 15, thus forming a paste or slurry film having a thickness prior to forming the barrier ribs 21 at step 33. In such a case, the formation of the barrier ribs 21 is performed through a screen print process, a sand blast process, an etching process, an additive process or a stamping process. The above processes for the formation of the barrier ribs 21 will be described later herein in more detail. Thereafter, the lower substrate 15, having the barrier ribs 21, is primarily baked at a temperature of 300.about.350.degree. C. for a predetermined time, for example, 15.about.23 minutes, thus removing the organic vehicle from the paste or slurry. The lower substrate 15 is, thereafter, secondarily baked at a temperature of 600.about.650.degree. C., thereby finally forming the barrier ribs 21.
The processes of the formation of such barrier ribs 21 will be described in detail hereinbelow with reference to FIGS. 3a to 3d.
FIG. 3a shows a screen printing process of the formation of such barrier ribs 21. As shown in the drawing, a screen (not shown) is primarily and precisely positioned on a lower substrate 40 coated with a thick dielectric film 41 on its top surface. A paste or slurry is applied on the top surface of the dielectric film 41 through the screen prior to being dried, thus forming a plurality of primary barrier rib layers 43 on the film 41 at step "a". The above-mentioned process is repeated several times, thus forming a plurality of secondary, third and more barrier rib layers on the previously formed layers at steps "b" and "c". A plurality of desired barrier ribs are thus formed on the lower substrate 40.
FIG. 3b shows a sand blast process of the formation of such barrier ribs 21. As shown in the drawing, a paste or slurry is applied on the top surface of a thick dielectric film 41, formed on the top surface of a lower substrate 40, thus forming a paste or slurry film 42 having a predetermined thickness, for example, 150.about.200 .mu.m, at step "a". A laminate film 45 is formed on the top surface of the paste or slurry film 42 at step "b". A laminate pattern 49 is, thereafter, formed on the paste or slurry film 42 through a lithography process using a mask 47 at steps "c" and "d". In such a case, the laminate film 45 is made of a tape-shaped material formed by addition of an organic or inorganic material to a photoresist material or a slurry at a given ratio. An abrasive material under pressure, such as sand, is blasted onto the top surface of the paste or slurry film 42 in a direction perpendicular to the laminate pattern 49, thus removing the paste or slurry from the film 42 at positions exposed to the atmosphere outside the pattern 49 at step "e". Thereafter, the laminate material is removed from the remaining paste or slurry, thus forming a plurality of desired barrier ribs 43 on the lower substrate 40 at step "f".
The steps of a conventional etching process of the formation of such barrier ribs 21 remain the same as that of the sand blast process, but the step "e" of removing the paste or slurry from the film 42 is performed by etching the film 42 using HCl, having a concentration of 5.about.10%, in place of the sand blasting step.
In the etching process or the sand blast process of forming such barrier ribs, it may be possible to form desired barrier ribs on the lower substrate by patterning the paste or slurry without using any separate photoresist laminate pattern when the paste or slurry film has photosensitivity itself.
FIG. 3c shows an additive process of the formation of such barrier ribs 21. As shown in the drawing, a laminate is applied on the top surface of a thick dielectric film 41, formed on the top surface of a lower substrate 40, thus forming a laminate film 50 having a predetermined thickness, for example, 150.about.200 .mu.m, at step "a". A laminate pattern 51 is, thereafter, formed on the lower substrate 40 through a lithography process using a mask 47 at step "b" and "c". In such a case, the laminate pattern 51 is opposed to a desired pattern of the barrier ribs 43. Thereafter, a paste or slurry 53 is applied to the top surface of the lower substrate 40 having the laminate pattern 51 on said top surface. The paste or slurry 53 on the lower substrate 40 is abraded until the top surface of the laminate pattern 51 is exposed to the atmosphere at step "d". At that step "d", the paste or slurry 53 is filled in the spaces between the laminate pattern 51. Thereafter, the paste or slurry 53 is dried. The laminate pattern 51 is, thereafter, removed from the top surface of the lower substrate 40, thus forming desired barrier ribs 43 on the lower substrate 40 at step "e".
FIG. 3d shows a stamping process of the formation of such barrier ribs 21. As shown in the drawing, a paste or slurry is applied to the top surface of a thick dielectric film 41, formed on the top surface of a lower substrate 40, thus forming a paste or slurry film 42 having a predetermined thickness, for example, 150.about.200 .mu.m, at step "a". Thereafter, a mold 55 is placed on the paste or slurry film 42, and a stamping step is performed at step "b". When the lower substrate 40 is made of glass, the stamping step is performed at a predetermined baking temperature. On the other hand, when the lower substrate 40 is made of metal, the stamping step is performed at room temperature. Thereafter, the mold 55 is removed from the lower substrate 40 at step "c", thus forming desired barrier ribs 43 on the substrate 40.
The characteristics of a conventional barrier rib fabricated through one of the above-mentioned processes are given in Table 3.
TABLE 3 Baking Dielectric Thermal Optical absortion Etching Temp. constant expansion rate rate (.degree. C.) (1 MHZ) coefficient (400 .about. 800 nm) (.mu.m/min.) 600 .about. 650 12 .about. 15 80 .about. 85 .times. 10.sup.-7 /.degree. 5 .about. 10% 4.0 (5% HCl)
As shown in the Table 3, the dielectric constant of such a conventional barrier rib has a range of 12.about.15, which is a high dielectric constant. Due to such a high dielectric constant, the barrier rib is problematic in that the addressing signal of the address electrode is retarded. Since PbO, or the basic component of the conventional barrier rib, has a high specific weight, the resulting PDP is undesirably heavy. In addition, the PbO may undesirably cause environmental pollution. It is also necessary for the conventional barrier rib to be baked at a high temperature of not less than 600.degree. C. and the conventional barrier rib has a thermal expansion coefficient of 80.about.85.times.10.sup.-7 /.degree. C. Therefore, when such a barrier rib is formed on a conventional glass substrate, the substrate may be undesirably deformed or cracked during a baking process. In the conventional process of fabricating such a barrier rib on a lower substrate, the thick film, made of paste or slurry, is reduced in its structural compactness due to an oxide filler, such as Al.sub.2 O.sub.3 and TiO.sub.2 mixture, added to the glass-ceramic material during a mixing process of preparing fine mixture powder. On the other hand, the conventional etching process of fabrication of the barrier ribs fails to form an evenly etched surface. The optical absorption rate of a conventional barrier rib is 5.about.10%, which does not reach a desirable rate, and so it is necessary to form a black matrix on the top surface of each barrier rib so as to improve the contrast of a resulting PDP. This complicates the structure of the PDP and results in a complicated process of fabricating such barrier ribs for PDPs.